refactor(ops): ops2 supports result in fast path (#19603)

Implements `Result` in fast-calls. Note that the approach here is
slightly different. Rather than store the last result in the `OpState`,
we put it into the `OpCtx` which saves us a lookup and lock in the error
case. We do not have to lock this field as it's guaranteed only one
runtime and thread can ever access it.

The fastcall path for many ops can avoid doing a great deal of work,
even for `Result` return values. In the previous iteration of `ops`, all
`Result`-returning functions would fetch and lock the `OpState`,
regardless of whether it was used or not.

2 files changed, 157 insertions, 62 deletions

diff --git a/core/ops.rs b/core/ops.rs
index a5c76e412..361fc3cb7 100644
--- a/core/ops.rs
+++ b/core/ops.rs
@@ -14,6 +14,7 @@ use futures::Future;
 use pin_project::pin_project;
 use serde::Serialize;
 use std::cell::RefCell;
+use std::cell::UnsafeCell;
 use std::ops::Deref;
 use std::ops::DerefMut;
 use std::ptr::NonNull;
@@ -106,7 +107,10 @@ pub fn to_op_result<R: Serialize + 'static>(
   }
 }
 
-// TODO(@AaronO): optimize OpCtx(s) mem usage ?
+/// Per-op context.
+///
+// Note: We don't worry too much about the size of this struct because it's allocated once per realm, and is
+// stored in a contiguous array.
 pub struct OpCtx {
   pub id: OpId,
   pub state: Rc<RefCell<OpState>>,
@@ -114,6 +118,8 @@ pub struct OpCtx {
   pub fast_fn_c_info: Option<NonNull<v8::fast_api::CFunctionInfo>>,
   pub runtime_state: Weak<RefCell<JsRuntimeState>>,
   pub(crate) context_state: Rc<RefCell<ContextState>>,
+  /// If the last fast op failed, stores the error to be picked up by the slow op.
+  pub(crate) last_fast_error: UnsafeCell<Option<AnyError>>,
 }
 
 impl OpCtx {
@@ -145,8 +151,35 @@ impl OpCtx {
       decl,
       context_state,
       fast_fn_c_info,
+      last_fast_error: UnsafeCell::new(None),
     }
   }
+
+  /// This takes the last error from an [`OpCtx`], assuming that no other code anywhere
+  /// can hold a `&mut` to the last_fast_error field.
+  ///
+  /// # Safety
+  ///
+  /// Must only be called from op implementations.
+  #[inline(always)]
+  pub unsafe fn unsafely_take_last_error_for_ops_only(
+    &self,
+  ) -> Option<AnyError> {
+    let opt_mut = &mut *self.last_fast_error.get();
+    opt_mut.take()
+  }
+
+  /// This set the last error for an [`OpCtx`], assuming that no other code anywhere
+  /// can hold a `&mut` to the last_fast_error field.
+  ///
+  /// # Safety
+  ///
+  /// Must only be called from op implementations.
+  #[inline(always)]
+  pub unsafe fn unsafely_set_last_error_for_ops_only(&self, error: AnyError) {
+    let opt_mut = &mut *self.last_fast_error.get();
+    *opt_mut = Some(error);
+  }
 }
 
 /// Maintains the resources and ops inside a JS runtime.
diff --git a/core/runtime/ops.rs b/core/runtime/ops.rs
index 76a29c5c3..84b578aeb 100644
--- a/core/runtime/ops.rs
+++ b/core/runtime/ops.rs
@@ -215,12 +215,15 @@ mod tests {
   use crate::JsRuntime;
   use crate::RuntimeOptions;
   use deno_ops::op2;
+  use std::cell::Cell;
 
   crate::extension!(
     testing,
     ops = [
+      op_test_fail,
       op_test_add,
       op_test_add_option,
+      op_test_result_void_switch,
       op_test_result_void_ok,
       op_test_result_void_err,
       op_test_result_primitive_ok,
@@ -228,47 +231,84 @@ mod tests {
     ]
   );
 
+  thread_local! {
+    static FAIL: Cell<bool> = Cell::new(false)
+  }
+
+  #[op2(core, fast)]
+  pub fn op_test_fail() {
+    FAIL.with(|b| {
+      println!("fail");
+      b.set(true)
+    })
+  }
+
   /// Run a test for a single op.
-  fn run_test(
+  fn run_test2(
+    repeat: usize,
     op: &'static str,
     test: &'static str,
-    f: impl FnOnce(Result<&v8::Value, anyhow::Error>, &mut v8::HandleScope),
-  ) {
+  ) -> Result<(), AnyError> {
     let mut runtime = JsRuntime::new(RuntimeOptions {
       extensions: vec![testing::init_ext()],
       ..Default::default()
     });
-    let value: Result<v8::Global<v8::Value>, anyhow::Error> = runtime
+    runtime
       .execute_script(
         "",
         FastString::Owned(
-          format!("const {{ {op} }} = Deno.core.ensureFastOps(); {test}")
-            .into(),
+          format!(
+            r"
+            const {{ op_test_fail, {op} }} = Deno.core.ensureFastOps();
+            function assert(b) {{
+              if (!b) {{
+                op_test_fail();
+              }}
+            }}
+          "
+          )
+          .into(),
         ),
-      );
-    let mut scope: v8::HandleScope =
-      // SAFETY: transmute for test (this lifetime should be safe for this purpose)
-      unsafe { std::mem::transmute(runtime.handle_scope()) };
-    match value {
-      Ok(value) => {
-        let value = value.open(&mut scope);
-        f(Ok(value), &mut scope)
-      }
-      Err(err) => f(Err(err), &mut scope),
+      )
+      .unwrap();
+    FAIL.with(|b| b.set(false));
+    runtime.execute_script(
+      "",
+      FastString::Owned(
+        format!(
+          r"
+      for (let __index__ = 0; __index__ < {repeat}; __index__++) {{
+        {test}
+      }}
+    "
+        )
+        .into(),
+      ),
+    )?;
+    if FAIL.with(|b| b.get()) {
+      Err(generic_error("test failed"))
+    } else {
+      Ok(())
     }
   }
 
+  #[tokio::test(flavor = "current_thread")]
+  pub async fn test_op_fail() {
+    assert!(run_test2(1, "", "assert(false)").is_err());
+  }
+
   #[op2(core, fast)]
   pub fn op_test_add(a: u32, b: u32) -> u32 {
     a + b
   }
 
-  #[tokio::test]
+  #[tokio::test(flavor = "current_thread")]
   pub async fn test_op_add() -> Result<(), Box<dyn std::error::Error>> {
-    run_test("op_test_add", "op_test_add(1, 11)", |value, scope| {
-      assert_eq!(value.unwrap().int32_value(scope), Some(12));
-    });
-    Ok(())
+    Ok(run_test2(
+      10000,
+      "op_test_add",
+      "assert(op_test_add(1, 11) == 12)",
+    )?)
   }
 
   #[op2(core)]
@@ -276,59 +316,84 @@ mod tests {
     a + b.unwrap_or(100)
   }
 
-  #[tokio::test]
+  #[tokio::test(flavor = "current_thread")]
   pub async fn test_op_add_option() -> Result<(), Box<dyn std::error::Error>> {
-    run_test(
+    // This isn't fast, so we don't repeat it
+    run_test2(
+      1,
       "op_test_add_option",
-      "op_test_add_option(1, 11)",
-      |value, scope| {
-        assert_eq!(value.unwrap().int32_value(scope), Some(12));
-      },
-    );
-    run_test(
+      "assert(op_test_add_option(1, 11) == 12)",
+    )?;
+    run_test2(
+      1,
       "op_test_add_option",
-      "op_test_add_option(1, null)",
-      |value, scope| {
-        assert_eq!(value.unwrap().int32_value(scope), Some(101));
-      },
-    );
+      "assert(op_test_add_option(1, null) == 101)",
+    )?;
     Ok(())
   }
 
-  #[op2(core)]
+  thread_local! {
+    static RETURN_COUNT: Cell<usize> = Cell::new(0);
+  }
+
+  #[op2(core, fast)]
+  pub fn op_test_result_void_switch() -> Result<(), AnyError> {
+    let count = RETURN_COUNT.with(|count| {
+      let new = count.get() + 1;
+      count.set(new);
+      new
+    });
+    if count > 5000 {
+      Err(generic_error("failed!!!"))
+    } else {
+      Ok(())
+    }
+  }
+
+  #[op2(core, fast)]
   pub fn op_test_result_void_err() -> Result<(), AnyError> {
     Err(generic_error("failed!!!"))
   }
 
-  #[op2(core)]
+  #[op2(core, fast)]
   pub fn op_test_result_void_ok() -> Result<(), AnyError> {
     Ok(())
   }
 
-  #[tokio::test]
+  #[tokio::test(flavor = "current_thread")]
   pub async fn test_op_result_void() -> Result<(), Box<dyn std::error::Error>> {
-    run_test(
+    // Test the non-switching kinds
+    run_test2(
+      10000,
       "op_test_result_void_err",
-      "op_test_result_void_err()",
-      |value, _scope| {
-        let js_error = value.err().unwrap().downcast::<JsError>().unwrap();
-        assert_eq!(js_error.message, Some("failed!!!".to_owned()));
-      },
-    );
-    run_test(
-      "op_test_result_void_ok",
-      "op_test_result_void_ok()",
-      |value, _scope| assert!(value.unwrap().is_null_or_undefined()),
-    );
+      "try { op_test_result_void_err(); assert(false) } catch (e) {}",
+    )?;
+    run_test2(10000, "op_test_result_void_ok", "op_test_result_void_ok()")?;
     Ok(())
   }
 
-  #[op2(core)]
+  #[tokio::test(flavor = "current_thread")]
+  pub async fn test_op_result_void_switch(
+  ) -> Result<(), Box<dyn std::error::Error>> {
+    RETURN_COUNT.with(|count| count.set(0));
+    let err = run_test2(
+      10000,
+      "op_test_result_void_switch",
+      "op_test_result_void_switch();",
+    )
+    .expect_err("Expected this to fail");
+    let js_err = err.downcast::<JsError>().unwrap();
+    assert_eq!(js_err.message, Some("failed!!!".into()));
+    assert_eq!(RETURN_COUNT.with(|count| count.get()), 5001);
+    Ok(())
+  }
+
+  #[op2(core, fast)]
   pub fn op_test_result_primitive_err() -> Result<u32, AnyError> {
     Err(generic_error("failed!!!"))
   }
 
-  #[op2(core)]
+  #[op2(core, fast)]
   pub fn op_test_result_primitive_ok() -> Result<u32, AnyError> {
     Ok(123)
   }
@@ -336,19 +401,16 @@ mod tests {
   #[tokio::test]
   pub async fn test_op_result_primitive(
   ) -> Result<(), Box<dyn std::error::Error>> {
-    run_test(
+    run_test2(
+      10000,
       "op_test_result_primitive_err",
-      "op_test_result_primitive_err()",
-      |value, _scope| {
-        let js_error = value.err().unwrap().downcast::<JsError>().unwrap();
-        assert_eq!(js_error.message, Some("failed!!!".to_owned()));
-      },
-    );
-    run_test(
+      "try { op_test_result_primitive_err(); assert(false) } catch (e) {}",
+    )?;
+    run_test2(
+      10000,
       "op_test_result_primitive_ok",
       "op_test_result_primitive_ok()",
-      |value, scope| assert_eq!(value.unwrap().int32_value(scope), Some(123)),
-    );
+    )?;
     Ok(())
   }
 }